Hitherto, from the points of mechanical strength and heat-resistant characteristics, a photoresist using a polyimide or a polyimide precursor has been practically used as a heat-resistant photoresist, and in particular, a negative-working photoresist forming desired relief images on various kinds of substrates by reducing solubility of the polyimide or polyimide precursor to a developer by irradiation of actinic rays has been mainly used.
Such heat-resistant photoresists each using negative-working photosensitive polyimide or the precursor thereof, which leave portions irradiated with actinic rays on each substrate, and the uses thereof are much proposed. For example, there are proposed (1) a method of introducing a methacryloyl group into a polyimide precursor via an ester bond or an ionic bond as described in JP-A-49-11541, JP-A-50-40992, JP-A-54-145794, JP-A-56-38038, etc., ("JP-A" as used herein means an "unexamined published Japanese patent application"), (2) a method of using a soluble polyimide having a photopolymerizing olefin as described in JP-A-59-108031, JP-A-59-220730, JP-A-59-232122, JP-A-60-6729, JP-A-60-72925, JP-A-61-57620, etc., and (3) a method of using a self-sensitizing type polyimide having a benzophenone skeleton and having an alkyl group at the ortho-position of the aromatic ring having bonded thereto a nitrogen atom as described in JP-A-59-219330, JP-A-59-231533, etc.
However, in the conventional negative-working photoresists using the above-described photosensitive polyimide or polyimide precursor, there is a problem in the function and the resolving power thereof and further, according to the uses thereof, there is a problem that the yield for the negative-working photoresist at the production thereof is lowered, etc. For example, in the heat-resistant photoresists produced in the method (1) described above, in the case of the ester bond-type photoresist, the synthesis is difficult, and in the case of the ionic bond-type photoresist, shrinkage occurs at imidation (heat curing). Also, in these heat-resistant photoresists, the thickness of the film or the layer of the photoresist is reduced at development, and the thickness of the residual film or layer after development and heat curing becomes about 50% of the initial thickness of the film or the layer. That is, there is a problem in the dimensional stability in these heat-resistant photoresists. Moreover, in the heat-resistant photoresists produced by the methods (2) and (3) described above, since the structure of the skeleton of the polymer used is limited, the properties of the coated layer or film finally obtained, whereby these photoresists cannot flexibly correspond to various required characteristics.
Further, since these photosensitive polyimides and polyimides precursors are insufficient in the point of light transmittance and, in particular, the light transmission factor in the film thickness direction is insufficient, several hundreds of mJ/cm.sup.2 are required as the amount of ultraviolet rays irradiating for forming patterns. As a result, the exposure time is prolonged and thus they have yet a problem in the point of productivity.
On the other hand, polycarbodiimide having a carbodiimide unit in the molecule is known as a resin excellent in heat resistance obtained by decarboxylation polycondensation of an isocyanate compound. By heating the resin, the carbodiimide bond in the molecule thereof causes a crosslinking reaction to improve the heat resistance of the resin.
Recently, a photosensitive composition obtained by compounding such a polycarbodiimide with an aromatic azide compound is proposed as described in JP-A-6-211956. However, this composition has the disadvantages that the composition is yet insufficient in the point of sensitivity, at the irradiation of the aromatic bisazide compound with light it is necessary to sufficiently consider the influence of oxygen, and thus, in the case of using the composition, the system is liable to be restricted in the apparatus. That is, since when a large amount of oxygen exists in the atmosphere at the light irradiation, nitrene formed by the light irradiation of the bisazide compound does not react with the polymer but preferentially reacts with oxygen to greatly lower the sensitivity of the composition, a deaerator becomes necessary at the light irradiation. Also, the coated film formed from the photosensitive composition compounded with an aromatic bisazide compound is greatly colored, and therefore it is difficult to use such a photosensitive composition in the field of requiring a transparency, such as a photosemiconductor device, LCD, etc. Further, there are the faults that the mechanism of the curing reaction is complicated, and the coated film becomes brittle and is poor in flexibility after the light irradiation.